1. Field of Invention
The present invention relates to a semiconductor device and a method for making the same, and particularly to a semiconductor chip mounted onto a tape substrate.
2. Description of Related Art
In the field of semiconductor devices, tape carrier packages (TCPs) are well known as one type of bare-chip-mounted packages. FIG. 5 is a schematic view of a film tape carrier. As shown in FIG. 5, the film tape carrier 30 is generally formed by laminating a copper foil onto a polyimide resin film, forming a circuit onto the copper foil, and plating thereon using Sn or Au, as an oblong product before the product is processed together with semiconductor devices. The lead comprises inner leads 20 bonded to an Au bump formed on an electrode pad of the semiconductor chip, and outer leads 36 integratedly formed with the inner leads 20 and used for connection to an exterior.
A method for making a TCP by a gang bonding process which simultaneously bonds all bumps to inner leads will now be described with reference to FIG. 6. A semiconductor chip is placed in a position surrounded by a device hole 32 on a stage (not shown in the drawing), and each bump of the semiconductor chip and the corresponding inner lead are aligned so that they are exactly bonded to each other. As shown in FIG. 6(1), a heating unit 52, which is preliminarily heated to about 500° C., is lowered toward the bumps and the inner leads 20 so that the heating unit 52 presses the bumps and the inner leads 20 on the stage.
The heat from the heating unit facilitates the formation of an Au/Sn eutectic alloy 46 shown in FIG. 6(2) by alloying the Au and the Sn plated on the inner leads 20. The mounting of the semiconductor chip 40 onto the film tape carrier 30 is completed by bonding the bumps to the inner leads 20 via the eutectic alloy 46. Next, unnecessary portions of the film tape carrier 30 are removed by punching to prepare a TCP.
However, the bonding of the bumps to the inner leads of the semiconductor chip using the heating unit has the following problems.
FIG. 4 is a schematic view showing a problem which occurs during mounting a semiconductor chip by a conventional technique. As shown in FIG. 4, a bump 10 is formed on an electrode pad 42 of a semiconductor chip 40. Since the periphery of the electrode pad 42 is covered by a passivation film 44 and protrudes, the bump 10 formed on the passivation film 44 also protrudes at the periphery and has an indented flat surface in the central portion. When the inner lead 20 is put into contact with the bump 10, a gap 18 is formed between the bump 10 and the inner lead 20 due to the protrusion. Thus, the central portion of the bump 10 does not contribute to the bonding of the bump 10 to the inner lead 20, in this state.
With reference to FIG. 6(2), in conventional thermal welding between the bump 10 and the inner lead 20, a high load and a high temperature are applied by the heating unit so that the Au/Sn eutectic alloy 46 is also formed in the central portion of the bump 10.
However, the application of the high load and the high temperature causes deforming and cracking of the inner lead and cracking of the passivation film. Such phenomena result in unreliability of the semiconductor devices as a product. Other problems, such as gas evolution from the film tape carrier and a shortened life of the heating unit, also arise.
Accordingly, it is an object of the present invention to provide a semiconductor device and a method for making the same in which bumps of a semiconductor chip and leads of a tape substrate can be securely bonded to each other by thermal welding using a heating unit.